#include <myheader_c_plus.h>
#include <cmath>
using namespace std;
using std::cout;
using std::endl;
class Point{
private:
    int _x;
    int _y;
public:
    Point(int x, int y)
    :_x(x)
    ,_y(y)
    {

    }
    friend class Line;
};

class Line{
public:
float distance(const Point & pt1, const Point & pt2){
    return sqrt( (pt1._x - pt2._x) * (pt1._x - pt2._x) + 
                 (pt1._y - pt2._y) * (pt1._y - pt2._y));        
}
    
};

int main(int argc, char *argv[])
{
    Point pt1(1,2);
    Point pt2(3,4);
    float dis;
    Line line;
    dis = line.distance(pt1, pt2);
    cout << dis << endl;
    return 0;
}

